1. Technical Field
The present invention relates generally to a stacked diode limiter and, more particularly, to a stacked diode limiter, which reduces the power intensity of a high-power interference pulse input to an in-band communication frequency band, thus protecting an electronic device arranged at the subsequent stage of an antenna in a wireless system.
2. Description of the Related Art
In the case of an operating frequency band of a wireless communication system, only signals in a specific band are transmitted without loss by a filter at an input stage and frequency signals out of the band are sufficiently attenuated by the filter.
However, when an interference pulse signal source, the frequency band of which is identical to that of the in-band communication frequency band, or the frequency band of which includes a part of the corresponding frequency band and which has a peak power of several hundreds of W to several tens of kW, is input to a wireless communication system through the antenna, a semiconductor device (in particular, the transistor part of a low-noise amplifier) connected to the subsequent stage of the antenna may be physically damaged or may malfunction (or be disordered) at such a predetermined power intensity or more.
An interference signal flowing into an in-band communication frequency band cannot be eliminated using only a filtering method. In order to prevent such an interference signal, a limiter device capable of non-linearly suppressing signals according to the intensity of input power is required.
Generally, a modular limiter device used in the antenna line of a wireless communication system or the like has a structure in which surface-mount diodes (SMD) are assembled on a planar board, and is typically operated within the range of input power of several tens of W. If the input power of the modular limiter device increases to several kW or more, an interval between the signal line of a microstrip line and a bottom ground layer is decreased, thus causing an electrical breakdown phenomenon. Further, when discharge caused by the electrical breakdown is continued, the board may be burned out or the conductor of a signal line may be melted.
Therefore, in order to prevent high-power interference signals of several kW or more, a waveguide-type transmission line other than a microstrip line, a strip line, a fin line, or a coplanar waveguide line, which uses a planar board, must be used.
However, such a waveguide structure is also disadvantageous in that when the frequency is decreased below several hundreds of MHz to several GHz, the size of the aperture of the waveguide is increased, and then the arrangement of the waveguide-type transmission line in the system is limited.
Prior art related to this technology includes a power limiter used at the previous stage of a low-noise amplifier (LNA) manufactured using a GaAs process. Such technology is disclosed in U.S. Pat. No. 6,853,264 entitled “Input power limiter for a microwave receiver,” in which multi-stage series/parallel diodes are assembled in different directions with respect to a transmission line, as shown in FIG. 1, thus improving power limitation performance. A structure in which elements are assembled on a transmission line in different directions is called an anti-parallel scheme, which denotes a scheme in which when diodes stacked on top of one another are connected to the upper and lower sides of a signal conductor for the transmission line, the anodes of the diodes are connected to one side of the transmission line signal conductor and the cathodes of the diodes are connected to the other side thereof, from the standpoint of the structure.
The structure of U.S. Pat. No. 6,853,264 is limited to the use of Schottky diodes without using PIN diodes typically used as limiter diodes. The reason for this is that it is impossible to integrate PIN diodes using the same process as that of a low-noise amplifier chip manufactured using a GaAs semiconductor process. Therefore, such a patent presents a scheme for utilizing Schottky diodes connected in series and in parallel to exhibit operating performance similar to that of PIN diodes even if the operating power characteristics thereof are not as good as the PIN diodes, thus improving operating power levels.
As shown in FIG. 1, technology disclosed in U.S. Pat. No. 6,853,264 presents a structure in which coarse limiters and fine limiters are arranged in a total of four stages in such a way that, in a first stage, 16 diodes are arranged in parallel and in series in a 4×4 array, in a second stage, 9 diodes are arranged in a 3×3 array, in a third stage, four diodes are arranged in a 2×2 array, and in a final stage, a single diode is connected. The diodes in all stages have an anti-parallel structure with respect to the transmission line, and the separation of individual stages is made using microstrip lines and inductors. In the design of a multi-stage limiter structure, a separation distance between individual stages must be a ¼ wavelength at the use frequency so as to prevent the impedances of the stages from influencing each other. In a semiconductor chip process, if ¼ wavelength is made using the length of only the microstrip line, the transmission line is excessively lengthened, so that the manufacture cost of chips is greatly increased, and thus inductors are employed as a method of compensating for an increase in the length of the line.
However, when such diodes are coupled to each other using inductors, high inductance occurs compared to the transmission line and high-frequency characteristics are limited, and thus there is a disadvantage in that a usable frequency band may be restricted.
Further, due to the operating power limits of Schottky diodes (having an input power limit of a total of 1 W or less) used for integration in a GaAs chip manufacturing process, even if a plurality of diodes are arranged in series and in parallel, the number of diodes that must be connected may reach several tens to several hundreds so as to operate even at pulse power of kW levels, thus greatly deviating from the original purpose of the limiter, that is, a previous stage protection circuit used in small-sized chips.
Further, a problem may arise in that, as the number of array diodes increases, the floating inductance and the floating capacitance of the circuit are continuously increased, and high-frequency impedance and insertion loss performance may be deteriorated, thus causing the use of the corresponding circuit to be greatly restricted.